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1950 8N No Fire


 
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muenster8n
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PostPosted: Thu Feb 08, 2018 1:14 pm    Post subject: 1950 8N No Fire Reply to specific post Reply with quote

All, as with several recent posts, I'm new to tractors in general. I recently took a 1950 8N on trade with a fairly nice brush hog. The tractor ran, but was very hard to start. I ran through a fairly typical "tune up" procedure as follows (questions at the bottom of the post).

- Pulled spark plugs (they were old). Caked with carbon, replaced with Autolite 437's gapped to .015
- I replaced the wires as the insulation was cracked
- Replaced the points, cap & rotor. Gapped points to .025
- Replaced battery (the old one would not hold a charge, tested bad)

I have not yet removed & cleaned the carb. I have not yet adjusted the carb (trying to diagnose one thing at a time). Now when I attempt to start the tractor, it appears that I get intermittent and/or no spark. I pulled one of the wires and attempt to get an arc across a ground while trying to start it and no spark. I got out my trusty multimeter and traced the various wires back to the battery source. On the lower side (distributor side) of the coil, I get an intermittent 6v. The system was converted to 12v battery source some years ago, but has a 6v coil. I replaced the coil with a 6v coil and re-measured. I get the same result: intermittent 6v. From the battery forward, I get 12v all the way to the main resistor. On the back side of the main resistor, I get an intermittent (sometimes non-existent) 12v. This appears to be the original resistor. So...

Question 1: Can the main resistor cause a no start by providing low or intermittent voltage to the coil? I'm not sure how sensitive the ignition + timing system is to voltage drops.

Question 2: The original exhaust was a vertical style with a rather large hole in it. I ordered a replacement that is a horizontal unit. Are they interchangeable?

As an aside, the tractor appears to be running very rich, but I'm trying to get it to a known state where it runs consistently before I start adjusting the fuel system.

Thanks!
 
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R Geiger
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PostPosted: Thu Feb 08, 2018 2:05 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

well to start with, which 8n do you have, is the dist on the front with a square coil or on the side with around coil.
second plugs should be gapped to 0.025" not 0.015"

front mount points are set to 0.015" side mount to 0.025"

You said 50 and that could be either of the two. You said original resistor that would only be on the front mount type dist.

If you have a round coil, you could get rid of the inline resistor if you installed a 12 volt coil. those inline resistors are all over the place in resistance.
It does sound like you have a late 50 tho with the round coil. The only time you will read voltage is with the points closed.
make sure you have ethe firing order correct, 1,2,4,3 front to back.
 
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doublebass73
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PostPosted: Thu Feb 08, 2018 2:07 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote


That coil needs a steady 6V in order for the tractor to run. Check the resistor with your ohmmeter, if it reads open then you need to replace the resistor. I don't have the specs in front of me but it should be a low resistance value if it's good.
 
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Bruce (VA)
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PostPosted: Thu Feb 08, 2018 2:09 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

Your plug gap is incorrect; it should be .025.

I assume you have a side distributor, correct?

Cut through the crap. Remove the resistor. Go to NAPA, get a 12v coil. IC14SB.

The coil does not have a "lower" side. The primary wires are marked + or - or BAT or IGN. Just wire the new coil with the negative side to the distributor because you now have a negative ground tractor.

" Question 1: Can the main resistor cause a no start by providing low or intermittent voltage to the coil? I'm not sure how sensitive the ignition + timing system is to voltage drops." Yes it sure can. But as I said, just get rid of the resistor. See tip # 30.

" I'm trying to get it to a known state where it runs consistently before I start adjusting the fuel system. "

I see you've done this stuff before! Some folks would have replaced half the parts on the tractor by now!

" Question 2: The original exhaust was a vertical style with a rather large hole in it. I ordered a replacement that is a horizontal unit. Are they interchangeable? " Yep. They all bolt to the manifold. Best get a new clamp & nuts too.
75 Tips

 
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muenster8n
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PostPosted: Thu Feb 08, 2018 2:31 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote


This a later model 8N with a side distributor and round coil. Duly noted on the plug gaps. I will adjust tomorrow morning. I will retest before touching anything else.

doublebass: I will measure the resistance on the existing unit. I have a new one in hand in the event that it reads open.

Bruce: if correcting the plug gap and the resistor doesn't work, I may do exactly that. I was attempting to avoid buy another new coil (I bought a brand new 6v coil last week). Duly noted on the exhaust clamp. I cracked the casting on the original one. I ordered a new one and it arrived this afternoon.

Thanks everyone for the quick responses! I'll report back tomorrow afternoon after wrenching on it a bit.
 
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Bruce (VA)
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PostPosted: Thu Feb 08, 2018 5:14 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

Even if the resistor is good, you still
don't know its value. Measure it. If it's
bad, compare the cost of a new resistor of
some unknown value to a new 12v coil.
75 Tips

 
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muenster8n
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PostPosted: Fri Feb 09, 2018 9:59 am    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

CVPost-Bruce (VA) wrote:
(quoted from post at 18:14:58 02/08/1Cool Even if the resistor is good, you still
don't know its value. Measure it. If it's
bad, compare the cost of a new resistor of
some unknown value to a new 12v coil.
75 Tips


Well, I re-gapped the plugs to the correct gap. I also tested the resistor and it was open. I had another one already handy, so I replaced it and we still have no start. I pulled one of the plug wires and fitting another plug so as to not lose compression, but watch the spark. No spark! I'm going to let it sit for a bit so as to not flood it any more and go back and retest everything with my meter.
 
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HFJ
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PostPosted: Fri Feb 09, 2018 11:37 am    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

muenster8n wrote:
(quoted from post at 13:59:09 02/09/1Cool
CVPost-Bruce (VA) wrote:
(quoted from post at 18:14:58 02/08/1Cool Even if the resistor is good, you still
don't know its value. Measure it. If it's
bad, compare the cost of a new resistor of
some unknown value to a new 12v coil.
75 Tips


Well, I re-gapped the plugs to the correct gap. I also tested the resistor and it was open. I had another one already handy, so I replaced it and we still have no start. I pulled one of the plug wires and fitting another plug so as to not lose compression, but watch the spark. No spark! I'm going to let it sit for a bit so as to not flood it any more and go back and retest everything with my meter.


take the resistor out of the circuit. even tho you've swapped it out for another one, that could still be your problem. try the ignition circuit without that resistor. it's an easy thing to do, and if u suddenly have spark, u have found your problem.

how many ohms in the "new" resistor?
 
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Ed S. (IL)
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PostPosted: Fri Feb 09, 2018 11:49 am    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

Just a thought, but also check your ignition switch - they go bad, too (see Bruce's tip #50).

es
 
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Bruce (VA)
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PostPosted: Fri Feb 09, 2018 4:24 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

OK, for the third time.....once from me earlier, once from HFJ and now from me again: you do not know the value of that resistor. Remove it from the circuit. If you have spark, then buy a 12v coil. Write off the cost as a learning experience, ;)

See tip # 30.
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muenster8n
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PostPosted: Fri Feb 09, 2018 4:56 pm    Post subject: Re: 1950 8N No Fire Reply to specific post Reply with quote

CVPost-Bruce (VA) wrote:
(quoted from post at 17:24:58 02/09/1Cool OK, for the third time.....once from me earlier, once from HFJ and now from me again: you do not know the value of that resistor. Remove it from the circuit. If you have spark, then buy a 12v coil. Write off the cost as a learning experience, Wink

See tip # 30.
75 Tips


We have lift off. I made sure all the connections were tight and remeasured the ballast resistor. It checked out ok. I went down the chair and looked for spark, nothing. Re-checked the firing order against the plug wires... Ugh... The wire to the coil and the wire to cylinder one were switched. I flipped them back and everything is right with the world again. Fired on the first try.

I won't comment who did this... Smile

On another note, horizontal exhaust is on. I made a few small fuel mixture adjustments and it runs much better. Thanks all for the help in diagnosing the issue.
 
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